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| United States Patent |
6,051,077
|
|
Sekine
, et al.
|
April 18, 2000
|
Raw material powder for modified permanent magnets and production method
of the same
Abstract
The present invention is directed to provide a raw material powder for
modified permanent magnets capable of enhancing magnetic properties of
iron.rare earth element metal.boron permanent magnets and reducing the
production cost, and further to provide its production method. The raw
material powder is a pulverized powder of sintered mass obtained by
sintering in vacuum or in a non-oxidative gas a mixture of an acicular
iron powder and an alloy powder containing iron, a rare earth element
metal and boron.
| Inventors:
|
Sekine; Shigenobu (Tokyo, JP);
Sato; Hiroji (Tokyo, JP)
|
| Assignee:
|
Sanei Kasei Co., Ltd. (Tokyo, JP)
|
| Appl. No.:
|
893991 |
| Filed:
|
July 16, 1997 |
Foreign Application Priority Data
| Current U.S. Class: |
148/105; 75/255; 148/302; 419/12 |
| Intern'l Class: |
H01F 001/057 |
| Field of Search: |
75/255
148/302,101,102,103,104,105
419/12
|
References Cited
U.S. Patent Documents
| 4601875 | Jul., 1986 | Yamamoto et al. | 419/23.
|
| 4802931 | Feb., 1989 | Croat | 148/302.
|
| 5443617 | Aug., 1995 | Takahashi | 75/254.
|
| 5478409 | Dec., 1995 | Takahashi | 148/104.
|
| 5569333 | Oct., 1996 | Takahashi | 148/105.
|
| 5728232 | Mar., 1998 | Takahashi | 148/105.
|
Primary Examiner: Sheehan; John
Attorney, Agent or Firm: Pillsbury Cushman & Sutro
Claims
What is claimed is:
1. A process of producing a raw material powder for modified permanent
magnets, wherein said process comprises steps of mixing 90-50 weight % of
an alloy powder containing iron, neodymium and boron with 10-50 weight %
of an acicular iron powder; sintering the resulting powdery mixture in
vacuum or in a non-oxidative gas; and pulverizing the resulting sintered
mass.
2. A process of producing a raw material powder for modified permanent
magnets according to claim 1, in which said step of sintering the powdery
mixture of an alloy powder containing iron, neodymium and boron mixed with
an acicular iron powder is carried out at 900-1200.degree. C.
3. A process of producing a raw material powder for modified permanent
magnets according to claim 1, in which said acicular iron powder is
obtained by reducing FeOOH (goethite) acicular crystal in a heated
hydrogen-containing gas.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a raw material powder for modified
permanent magnets superior in magnetic properties, and to a process for
producing the raw material powder.
2. Description of the Prior Art
Permanent magnets containing iron and rare earth element metals, especially
rare earth element metal.iron.boron permanent magnets, are praised for
their superior magnetic properties. JP-B-61-34242 discloses magnetically
anisotropic sintered magnets having Fe-B-Nd components. The production
method includes preparing a cast alloy containing the above components,
pulverizing the cast alloy and molding-sintering the alloy powder, for
which pulverization of the cast alloy costs much.
SUMMARY OF THE INVENTION
The present invention is directed to provide a raw material powder for
modified permanent magnets capable of enhancing magnetic properties of
iron.rare earth element metal-boron permanent magnets and reducing the
production cost, and further to provide its production method.
A raw material powder for modified permanent magnets according to the
present invention comprises a pulverized powder of sintered mass obtained
by sintering in vacuum or in a non-oxidative gas a mixture of an acicular
iron powder and an alloy powder containing iron, a rare earth element
metal and boron. And the process of producing a raw material powder for
modified permanent magnets comprises steps of mixing an alloy powder
containing iron, a rare earth element metal and boron with an acicular
iron powder; sintering the resulting powdery mixture in vacuum or in a
non-oxidative gas; and pulverizing the resulting sintered mass.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing magnetic properties of a sintered magnet prepared
from a pulverized powder of sintered mass obtained by sintering a mixture
of alloy powder A and an acicular iron powder.
FIG. 2 is a graph showing magnetic properties of a sintered magnet prepared
from a pulverized powder of sintered mass obtained by sintering a mixture
of alloy powder B and an acicular iron powder.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The alloy powder containing iron, a rare earth element metal and boron used
for the present invention may be any alloy powder of known composition
capable of exhibiting strong magnetism when formed into sintered magnets
or bonded magnets. As for the rare earth element metal (referred to as
RE), neodium (Nd) and praseodymium (Pr) are praised. As for the alloys are
included Fe.RE.B system and Fe.RE.B.C system, and alloys containing
further at least one component selected from Ti, V, Cr, Mn, Ni, Zr, Nb,
Mo, Hf, Ta, W, Pd, Ag, Pt, Au, Al, Cu, Ga, In, Sn, Sb, Pb, Bi, Zn, P, Si,
Ge and S are known. The alloy powder is obtainable by preparing firstly an
alloy of desired composition and then pulverizing the alloy mechanically
or by hydrogen-disintegration methods, though commercially available
products can be used. In either case, magnetic properties of magnets using
the alloy powder are improved when the alloy powder is used after it is
mixed with an acicular iron powder, the mixture is sintered, and the
sintered mass is pulverized. The alloy powder preferably has an average
particle size of micron (.mu.m) order.
The acicular iron powder is obtained by reducing FeOOH (goethite) with
hydrogen under hydrogen atmosphere heated at 300-500.degree. C. An
acicular iron powder having a length not longer than 10 .mu.m and a width
of around one tenth of the length is preferred. Co component may be
incorporated when producing the acicular iron powder.
Mixing ratios of the alloy powder containing iron, the rare earth element
metal and boron to the acicular iron powder is preferably 90-10 weight %
of the alloy powder containing iron, the rare earth element metal and
boron to 10-90 weight % of the acicular iron powder, and 90-50 weight % of
the alloy powder to 10-50 weight % of the acicular iron powder can
specifically exhibit enhanced magnetic properties due to synergetic
effects (see Table 2 and Figures attached).
Sintering of the powder mixture is carried out in vacuum or in a
non-oxidative gas to avoid oxidation of the powder mixture. The
temperature for sintering the powder mixture is preferably
900-1200.degree. C. The sintered mass is pulverized under such
non-oxidative atmosphere as vacuum, in a non-oxidative gas or in an inert
medium.
The present invention will be described in detail hereunder by reference to
Examples, however, the invention shall never be restricted to the
Examples.
EXAMPLES AND COMPARATIVE EXAMPLES
Each alloy powder (average particle size was smaller than 1 .mu.m) A and B
mentioned in Table 1 was mixed with an acicular iron powder having 0.2
.mu.m length and 0.02 .mu.m width to obtain mixtures containing 10, 20,
30, 40, 50, 70 and 90 weight % of the acicular iron powder. The powdery
mixture was sintered at 1000.degree. C. in vacuum (10.sup.-6 Torr), and
the resulting sintered mass was pulverized to obtain the raw material
powder. The resulting raw material powder (Example), each of the alloy
powder A and B itself (Comparative Example) and the acicular iron powder
itself (Comparative Example) were subjected to molding under 3 t/cm.sup.2
pressure and 10 KOe magnetic field followed by sintering for 1 hour at
1000.degree. C. in vacuum and aging, and permanent magnets were obtained.
For those resulting permanent magnets were measured the Maximum Energy
Product (BHmax), Residual Flux Density (Br) and Coercive Force (iHc). The
result of measurement is shown in Table 2 and FIGS. 1-2 (.quadrature.:Br,
.DELTA.:iHc, .smallcircle.: BHmax).
TABLE 1
______________________________________
Composition of
alloy powder
(weight %)
A B
______________________________________
Fe 52.0 84.3
Nd 28.0 8.7
Pr 4.0
B 1.0 0.7
Cu 0.1
V 0.3
Co 15.0 5.8
Ni 0.1
Total 100.0 100.0
______________________________________
As understandable from Table 2 and FIGS. 1-2, the sintered magnet made from
the raw material powder for modified permanent magnets according to the
invention, which raw material powder is prepared by pulverizing sintered
mass of the acicular iron powder and the alloy powder A or B can exhibit
more superior magnetic properties than sintered magnets made singly from
each of the alloy powder A or B (Comparative Examples) or from the
acicular iron powder (Comparative Example).
It is possible to obtain a raw material powder for modified permanent
magnets exhibiting improved magnetic properties than those made singly
from a raw material powder composed of an alloy powder containing iron and
rare earth element metals. Further, the invention decreases the amount of
the expensive alloy containing rare earth element metals to result in a
reduced production cost.
TABLE 2
______________________________________
weight %
Acicular Alloy powder
Iron Properties A B
______________________________________
0 Br (KG) 12.01
10.35
Comparative iHc (KOe) 9.13
8.73
Example BHmax (MGOe) 40 35
10 Br (KG) 17.77
12.98
Example iHc (KOe) 10.13
13.87
BHmax (MGOe) 60 60
20 Br (KG) 17.90
12.09
Example iHc (KOe) 11.02
12.65
BHmax (MGOe) 63 51
30 Br (KG) 17.79
12.39
Example iHc (KOe) 10.98
12.83
BHmax (MGOe) 61 53
40 Br (KG) 18.00
10.75
Example iHc (KOe) 11.05
10.76
BHmax (MGOe) 63 40
50 Br (KG) 18.47
11.86
Example iHc (KOe) 11.54
11.00
BHmax (MGOe) 65 45
70 Br (KG) 16.19
11.10
Example iHc (KOe) 9.27
10.81
BHmax (MGOe) 50 40
90 Br (KG) 14.77
10.91
Example iHc (KOe) 8.13
10.72
BHmax (MGOe) 40 39
100 Br (KG) 14.40
Comparative iHc (KOe) 1.65
Example BHmax (MGOe) 9.5
______________________________________
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